Pennsylvania’s Sen. Arlen Specter, who announced his switch from the Republican to the Democratic Party today, will remain a key swing vote in a Senate locked by GOP filibusters on green economy legislation like cap and trade, renewable energy standards, and green jobs programs. Specter will be joining a bloc of conservative Democratic senators who are publicly skeptical of President Obama’s clean energy agenda, and who have repeatedly voted against Obama’s proposal to place limits on global warming pollution:

Ideologically, Specter is in line with Democrats like Sen. Evan Bayh (D-IN), who worries that Obama’s clean economy proposal may “suck money” from his state, Sen. Mary Landrieu (D-LA), who is “against forcing petrochemical companies” to “bear the brunt of new costs,” and Sen. Ben Nelson (D-NE), who worries cap and trade “could have a negative impact on our economy.”